Merge branch 'bpf-allow-bpf_for_each_map_elem-helper-with-different-input-maps'

Philo Lu says:

====================
bpf: allow bpf_for_each_map_elem() helper with different input maps

Currently, taking different maps within a single bpf_for_each_map_elem
call is not allowed. For example the following codes cannot pass the
verifier (with error "tail_call abusing map_ptr"):
```
static void test_by_pid(int pid)
{
	if (pid <= 100)
		bpf_for_each_map_elem(&map1, map_elem_cb, NULL, 0);
	else
		bpf_for_each_map_elem(&map2, map_elem_cb, NULL, 0);
}
```

This is because during bpf_for_each_map_elem verifying,
bpf_insn_aux_data->map_ptr_state is expected as map_ptr (instead of poison
state), which is then needed by set_map_elem_callback_state. However, as
there are two different map ptr input, map_ptr_state is marked as
BPF_MAP_PTR_POISON, and thus the second map_ptr would be lost.
BPF_MAP_PTR_POISON is also needed by bpf_for_each_map_elem to skip
retpoline optimization in do_misc_fixups(). Therefore, map_ptr_state and
map_ptr are both needed for bpf_for_each_map_elem.

This patchset solves it by transform bpf_insn_aux_data->map_ptr_state as a
new struct, storing poison/unpriv state and map pointer together without
additional memory overhead. Then bpf_for_each_map_elem works well with
different input maps. It also makes map_ptr_state logic clearer.

A test case is added to selftest, which would fail to load without this
patchset.

Changelogs
-> v1:
- PATCH 1/3:
  - make the commit log clearer
  - change poison and unpriv to bool in struct bpf_map_ptr_state, also the
    return value in bpf_map_ptr_poisoned() and bpf_map_ptr_unpriv()
- PATCH 2/3:
  - change the comments in set_map_elem_callback_state()
- PATCH 3/3:
  - remove the "skipping the last element" logic during map updating
  - change if() to ASSERT_OK()

Please review, thanks.
====================

Link: https://lore.kernel.org/r/20240405025536.18113-1-lulie@linux.alibaba.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -502,6 +502,13 @@ struct bpf_loop_inline_state {
 	u32 callback_subprogno; /* valid when fit_for_inline is true */
 };
 
+/* pointer and state for maps */
+struct bpf_map_ptr_state {
+	struct bpf_map *map_ptr;
+	bool poison;
+	bool unpriv;
+};
+
 /* Possible states for alu_state member. */
 #define BPF_ALU_SANITIZE_SRC		(1U << 0)
 #define BPF_ALU_SANITIZE_DST		(1U << 1)
@@ -514,7 +521,7 @@ struct bpf_loop_inline_state {
 struct bpf_insn_aux_data {
 	union {
 		enum bpf_reg_type ptr_type;	/* pointer type for load/store insns */
-		unsigned long map_ptr_state;	/* pointer/poison value for maps */
+		struct bpf_map_ptr_state map_ptr_state;
 		s32 call_imm;			/* saved imm field of call insn */
 		u32 alu_limit;			/* limit for add/sub register with pointer */
 		struct {

kernel/bpf/verifier.c

@@ -190,11 +190,6 @@ struct bpf_verifier_stack_elem {
 #define BPF_MAP_KEY_POISON	(1ULL << 63)
 #define BPF_MAP_KEY_SEEN	(1ULL << 62)
 
-#define BPF_MAP_PTR_UNPRIV	1UL
-#define BPF_MAP_PTR_POISON	((void *)((0xeB9FUL << 1) +	\
-					  POISON_POINTER_DELTA))
-#define BPF_MAP_PTR(X)		((struct bpf_map *)((X) & ~BPF_MAP_PTR_UNPRIV))
-
 #define BPF_GLOBAL_PERCPU_MA_MAX_SIZE  512
 
 static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx);
@@ -209,21 +204,22 @@ static bool is_trusted_reg(const struct bpf_reg_state *reg);
 
 static bool bpf_map_ptr_poisoned(const struct bpf_insn_aux_data *aux)
 {
-	return BPF_MAP_PTR(aux->map_ptr_state) == BPF_MAP_PTR_POISON;
+	return aux->map_ptr_state.poison;
 }
 
 static bool bpf_map_ptr_unpriv(const struct bpf_insn_aux_data *aux)
 {
-	return aux->map_ptr_state & BPF_MAP_PTR_UNPRIV;
+	return aux->map_ptr_state.unpriv;
 }
 
 static void bpf_map_ptr_store(struct bpf_insn_aux_data *aux,
-			      const struct bpf_map *map, bool unpriv)
+			      struct bpf_map *map,
+			      bool unpriv, bool poison)
 {
-	BUILD_BUG_ON((unsigned long)BPF_MAP_PTR_POISON & BPF_MAP_PTR_UNPRIV);
 	unpriv |= bpf_map_ptr_unpriv(aux);
-	aux->map_ptr_state = (unsigned long)map |
-			     (unpriv ? BPF_MAP_PTR_UNPRIV : 0UL);
+	aux->map_ptr_state.unpriv = unpriv;
+	aux->map_ptr_state.poison = poison;
+	aux->map_ptr_state.map_ptr = map;
 }
 
 static bool bpf_map_key_poisoned(const struct bpf_insn_aux_data *aux)
@@ -9655,12 +9651,8 @@ static int set_map_elem_callback_state(struct bpf_verifier_env *env,
 	struct bpf_map *map;
 	int err;
 
-	if (bpf_map_ptr_poisoned(insn_aux)) {
-		verbose(env, "tail_call abusing map_ptr\n");
-		return -EINVAL;
-	}
-
-	map = BPF_MAP_PTR(insn_aux->map_ptr_state);
+	/* valid map_ptr and poison value does not matter */
+	map = insn_aux->map_ptr_state.map_ptr;
 	if (!map->ops->map_set_for_each_callback_args ||
 	    !map->ops->map_for_each_callback) {
 		verbose(env, "callback function not allowed for map\n");
@@ -10019,12 +10011,12 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
 		return -EACCES;
 	}
 
-	if (!BPF_MAP_PTR(aux->map_ptr_state))
+	if (!aux->map_ptr_state.map_ptr)
 		bpf_map_ptr_store(aux, meta->map_ptr,
-				  !meta->map_ptr->bypass_spec_v1);
-	else if (BPF_MAP_PTR(aux->map_ptr_state) != meta->map_ptr)
-		bpf_map_ptr_store(aux, BPF_MAP_PTR_POISON,
-				  !meta->map_ptr->bypass_spec_v1);
+				  !meta->map_ptr->bypass_spec_v1, false);
+	else if (aux->map_ptr_state.map_ptr != meta->map_ptr)
+		bpf_map_ptr_store(aux, meta->map_ptr,
+				  !meta->map_ptr->bypass_spec_v1, true);
 	return 0;
 }
 
@@ -19840,7 +19832,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			    !bpf_map_ptr_unpriv(aux)) {
 				struct bpf_jit_poke_descriptor desc = {
 					.reason = BPF_POKE_REASON_TAIL_CALL,
-					.tail_call.map = BPF_MAP_PTR(aux->map_ptr_state),
+					.tail_call.map = aux->map_ptr_state.map_ptr,
 					.tail_call.key = bpf_map_key_immediate(aux),
 					.insn_idx = i + delta,
 				};
@@ -19869,7 +19861,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 				return -EINVAL;
 			}
 
-			map_ptr = BPF_MAP_PTR(aux->map_ptr_state);
+			map_ptr = aux->map_ptr_state.map_ptr;
 			insn_buf[0] = BPF_JMP_IMM(BPF_JGE, BPF_REG_3,
 						  map_ptr->max_entries, 2);
 			insn_buf[1] = BPF_ALU32_IMM(BPF_AND, BPF_REG_3,
@@ -19977,7 +19969,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			if (bpf_map_ptr_poisoned(aux))
 				goto patch_call_imm;
 
-			map_ptr = BPF_MAP_PTR(aux->map_ptr_state);
+			map_ptr = aux->map_ptr_state.map_ptr;
 			ops = map_ptr->ops;
 			if (insn->imm == BPF_FUNC_map_lookup_elem &&
 			    ops->map_gen_lookup) {

tools/testing/selftests/bpf/prog_tests/for_each.c

@@ -5,6 +5,7 @@
 #include "for_each_hash_map_elem.skel.h"
 #include "for_each_array_map_elem.skel.h"
 #include "for_each_map_elem_write_key.skel.h"
+#include "for_each_multi_maps.skel.h"
 
 static unsigned int duration;
 
@@ -143,6 +144,65 @@ static void test_write_map_key(void)
 		for_each_map_elem_write_key__destroy(skel);
 }
 
+static void test_multi_maps(void)
+{
+	struct for_each_multi_maps *skel;
+	__u64 val, array_total, hash_total;
+	__u32 key, max_entries;
+	int i, err;
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 1,
+	);
+
+	skel = for_each_multi_maps__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "for_each_multi_maps__open_and_load"))
+		return;
+
+	array_total = 0;
+	max_entries = bpf_map__max_entries(skel->maps.arraymap);
+	for (i = 0; i < max_entries; i++) {
+		key = i;
+		val = i + 1;
+		array_total += val;
+		err = bpf_map__update_elem(skel->maps.arraymap, &key, sizeof(key),
+					   &val, sizeof(val), BPF_ANY);
+		if (!ASSERT_OK(err, "array_map_update"))
+			goto out;
+	}
+
+	hash_total = 0;
+	max_entries = bpf_map__max_entries(skel->maps.hashmap);
+	for (i = 0; i < max_entries; i++) {
+		key = i + 100;
+		val = i + 1;
+		hash_total += val;
+		err = bpf_map__update_elem(skel->maps.hashmap, &key, sizeof(key),
+					   &val, sizeof(val), BPF_ANY);
+		if (!ASSERT_OK(err, "hash_map_update"))
+			goto out;
+	}
+
+	skel->bss->data_output = 0;
+	skel->bss->use_array = 1;
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.test_pkt_access), &topts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
+	ASSERT_OK(topts.retval, "retval");
+	ASSERT_EQ(skel->bss->data_output, array_total, "array output");
+
+	skel->bss->data_output = 0;
+	skel->bss->use_array = 0;
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.test_pkt_access), &topts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
+	ASSERT_OK(topts.retval, "retval");
+	ASSERT_EQ(skel->bss->data_output, hash_total, "hash output");
+
+out:
+	for_each_multi_maps__destroy(skel);
+}
+
 void test_for_each(void)
 {
 	if (test__start_subtest("hash_map"))
@@ -151,4 +211,6 @@ void test_for_each(void)
 		test_array_map();
 	if (test__start_subtest("write_map_key"))
 		test_write_map_key();
+	if (test__start_subtest("multi_maps"))
+		test_multi_maps();
 }

tools/testing/selftests/bpf/progs/for_each_multi_maps.c

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 3);
+	__type(key, __u32);
+	__type(value, __u64);
+} arraymap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 5);
+	__type(key, __u32);
+	__type(value, __u64);
+} hashmap SEC(".maps");
+
+struct callback_ctx {
+	int output;
+};
+
+u32 data_output = 0;
+int use_array = 0;
+
+static __u64
+check_map_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+	       struct callback_ctx *data)
+{
+	data->output += *val;
+	return 0;
+}
+
+SEC("tc")
+int test_pkt_access(struct __sk_buff *skb)
+{
+	struct callback_ctx data;
+
+	data.output = 0;
+	if (use_array)
+		bpf_for_each_map_elem(&arraymap, check_map_elem, &data, 0);
+	else
+		bpf_for_each_map_elem(&hashmap, check_map_elem, &data, 0);
+	data_output = data.output;
+
+	return 0;
+}